X-Ray technology reveals woman hidden behind Edgar Degas portrait

Australian researchers have used X-ray fluorescence to find a figure hidden underneath a 19th century portrait by French impressionist Edgar Degas.

Portrait of a Woman, painted between 1876 and 1880, has long been known to have a concealed painting underneath its surface, but the details have always been a mystery — until now.

By applying a non-invasive, rapid, high-definition X-ray fluorescence (XRF) mapping technique, scientist Daryl Howard, from the Australian Synchrotron, and fellow researchers were able to reveal the hidden woman in clear detail.

"Then we have a X-ray fluorescence detector that operates very quickly so we can scan the painting through that beam quite rapidly, and collect the elemental information of the painting as we are scanning it."

It has been discovered that by using the XRF technique, metallic elements from pigments in an underpainting can be detected, enabling the reconstruction of hidden layers.

"Each metal has its own unique X-ray energy that it gives off as it gets excited so we collect that with the detector."

The false colour effect was achieved by using custom-made software which then produces a plausible representation of the artist's work.

If the reconstruction had been attempted 10 years previously, it would have taken over a year but due to current technology, the researchers were able to scan the painting in just a day and a half.

The technology is used for a wide range of purposes including disease studies, food nutrition research and geological exploration.

"The scanning of paintings is a very fun thing we do but not something we do everyday," Dr Howard said.

Receiving the Degas original was "very exciting", Mr Howard said, but the special privilege of actually handling the painting was left to conservators from the National Gallery of Victoria who mounted the painting in the machine.

The technological advancements for examining artwork using synchrotron radiation-based techniques are certain to transform the way art is studied and interpreted, Dr Howard said.

"I think it's a really powerful analytical tool that is really going to help conservators.

"The technique is pretty well established but now that commercial scanners are coming out to do this kind of work I think it's really going to take off and we are going to see a lot more of it.

"In the early days of this technique, somebody had to be quite an expert in it and basically build their own system which was a very difficult task, but now you can actually order one from a company and do it in a gallery."

The process allows a significantly greater understanding of an artist's work for preservation and scholarly purposes.

Concealed paintings can also reveal the evolution of an artist's technique and evoke many theories as to why an artist chose to cover up an early composition.

"I wonder if Degas would ever think people, centuries down the road, would look underneath the painting and see what he originally put on the canvas, Dr Howard said.

"In his later years the technique of X-raying paintings was known so whether he was aware of that I'm not sure."

"Painting over" was a common technique in Degas' time as, depending on how poor an artist was, they would simply paint over a painting if they did not like it to save buying a new canvas.

Portrait of a Woman is on display at the National Gallery of Victoria.

A report detailing the process Dr Howard and his colleagues underwent has been published in the journal Scientific Reports.